1. Field of the Invention
The present invention generally relates to a subrack device, and more particularly to a subrack device which is used in a communication system based on an SDH (Synchronous Digital Hierarchy).
There are various specifications for communication system based on the SDH. A subrack device which is used in the communication system based on the SDH is required to have a performance in response to a particular specification of the communication system. However, to reduce the production cost, the subrack device is required to be produced flexibly to handle any one of the various specifications of the subrack device.
2. Description of the Prior Art
One example of the communication system based on the SDH will now be described. FIG. 1 shows a communication system 10 based on the SDH. In FIG. 1, a network (LINE (a high-order group)) 10A based on the SDH is shown. Also, in FIG. 1, telephone stations 11.sub.-1 -11.sub.-4 are shown. Subrack devices 12 of the present invention are installed in the telephone stations 11.sub.1 -11.sub.-4. The telephone stations 11.sub.-1 -11.sub.-4 communicate through optical-fibers 13. Each of the telephone stations 11.sub.-1 -11.sub.-4 has a non-synchronizing hierarchy network 15 (TRIB (a low-order group)). The non-synchronizing hierarchy network 15 comprises a non-synchronizing hierarchy network device17 connected to the subrack device 12, a power-source 16 and a telephone device 18.
The communication system 10, as described above, has the network (LINE (a high-order group)) 11 based on the SDH and the non-synchronizing hierarchy network 15 (TRIB (a low-order group)). The communication system 10 classifies communication systems 10.sub.-1 -10.sub.-13 shown in FIG. 2, based on a fundamental bit rate for multiplying signals. As shown in FIG. 2, the communication system 10.sub.-1 comprises a synchronizing network 10A having a fundamental bit rate of 155 Mbps, and a non-synchronizing network 15 having a fundamental bit rate of 2 Mbps and an impedance of 75.OMEGA.. The communication system 10.sub.-2 comprises a synchronizing network having a fundamental bit rate of 155 Mbps, and a non-synchronizing network having a fundamental bit rate of 2 Mbps and an impedance of 120.OMEGA.. The communication system 10.sub.-3 comprises a synchronizing network having a fundamental bit rate of 622 Mbps, and a non-synchronizing network having a fundamental bit rate of 2 Mbps and an impedance of 75.OMEGA.. The communication system 10.sub.-4 comprises a synchronizing network in which a fundamental bit rate is 622 Mbps and a non-synchronizing network in which a fundamental bit rate is 2 Mbps and an impedance is 120.OMEGA.. The communication system 10.sub.-7 comprises a synchronizing network in which a fundamental bit rate is 622 Mbps and a non-synchronizing network in which a fundamental bit rate is 34 Mbps and an impedance is 75.OMEGA..
FIGS. 3A, 3B and 3C are schematic illustrations showing a subrack device applicable for the communication system 10.sub.-1 shown in FIG. 2. More particularly, FIG. 3A is a perspective view showing a subrack device, FIG. 3B is a perspective view showing a back-wiring-board (BWB) assembly and FIG. 3C is a circuit diagram showing a circuit-board-unit.
As shown in FIG. 4A, the subrack device 20.sub.-1 has a subrack body 21.sub.-1 in which a plurality of circuit-board-units 22.sub.-1 are mounted. The subrack body 21.sub.-1 has a chassis assembly 23.sub.-1 made of a metal plate, and a back-wiring-board (BWB) assembly 24.sub.-1 is incorporated therein. The subrack body 21.sub.-1 has a box-shaped circuit-board-unit housing portion 25.sub.-1 and an outer connector arranging portion 26.sub.-1 standing at a back face of the circuit-board-unit housing portion 25.sub.-1. The BWB assembly 24.sub.-1 has a BWB 27.sub.-1 in which connectors 28.sub.-1, 29.sub.-1 for the circuit-board-units, a power-source receiving connector 30.sub.-1 and an outer connector 31.sub.-1 are mounted. The circuit-board-unit 22.sub.-1 has a 75.OMEGA. impedance conversion transformer 32.sub.-1, as shown in FIG. 4C. The subrack device 20.sub.-1 is used in the communication system 10.sub.-1 and is installed in the telephone station 11.sub.-1 in FIG. 1. The optical-fiber 13 is connected to the circuit-board-unit 22.sub.-1 and an electrical wire 16.sub.-1 is connected to the outer connector 31.sub.-1 for an operation.
FIGS. 4A, 4B and 4C are schematic illustrations showing a subrack device applicable for the communication system 10.sub.-2 shown in FIG. 2. More particularly, FIG. 4A is a perspective view showing a subrack device, FIG. 4B is a perspective view showing a back-wiring-board (BWB) assembly and FIG. 4C is a circuit diagram showing a circuit-board-unit.
As shown in FIG. 4A, the subrack device 20.sub.-2 has a subrack body 21.sub.-2 in which a plurality of circuit-board-units 22.sub.-2 are mounted. The subrack body 21.sub.-2 has a chassis assembly 23.sub.-2 made of a metal plate and a back-wiring-board (BWB) assembly 24.sub.-2 is incorporated therein. The subrack body 21.sub.-2 has a box-shaped circuit-board-unit housing portion 25.sub.-2 and an outer connector arranging portion 26.sub.-2 standing at a back face of the circuit-board-unit housing portion 25.sub.-2. The BWB assembly 24.sub.-2 has a BWB 27.sub.-2 in which the connectors 28.sub.-1, 291 for the circuit-board-unit, the power-source receiving connector 30.sub.-1 and an outer connector 31.sub.-2 are mounted. The circuit-board-unit 22.sub.-2 has a 120.OMEGA. impedance conversion transformer 32.sub.-2, as shown in FIG. 4C. The subrack device 20.sub.-2 is used in the communication system 10.sub.-2 and is installed in the telephone station 11.sub.-2 in FIG. 1. The optical-fiber 13 is connected to the circuit-board-unit 22.sub.-2 and the electrical wire 16.sub.-2 is connected to the outer connector 31.sub.-2 for an operation.
As is understood from the above description, a manufacturer has to design and produce different types of the chassis body 23.sub.-1 (23.sub.-2), the BWB assembly 24.sub.-1 (240.sub.-2) and the circuit-board-unit 22.sub.-1 (22.sub.-2) for each communication system. Therefore, the production cost of the subrack device is high.